1. Field of the Invention
The present invention relates to a fuel injection apparatus for an internal combustion engine, more particularly to an improved spill mechanism by which the fuel pressure within the pumping chamber of such internal combustion engine is reduced to stop the supply of fuel to the fuel injection valve.
2. Description of the Prior Art
In a fuel injection apparatus like a fuel injection pump, fuel injection is usually stopped by spilling the fuel from the pumping chamber to the fuel reservoir at a selected time during the ejection stroke of the pump, thereby reducing the pressure within the pumping chamber. In recent years, many proposals have been made to adopt a solenoid valve in such mechanisms for the purpose of spilling the fuel from the pumping chamber to the fuel reservoir. These proposals were made to allow electronic control of the amount of fuel injection from the fuel injection valve.
In such conventional spill mechanisms, however, if the aperture area or lift amount of the solenoid valve is made large for a sufficient spill amount of fuel, the response is correspondingly reduced. Also, the solenoid valve itself would have a rather large volume, which is not desirable from a structural viewpoint.
Furthermore, with prior art spill mechanism, as it is impossible to precisely sense when fuel was supplied to the fuel injection valve, the operation of the solenoid valve cannot be feedback-controlled. More particularly, the performance varies from one solenoid valve to another. Such performance variation cannot be eliminated and reflects directly upon the performance of fuel supply apparatus. As a result, it is impossible to control the supply amount of fuel with a high accuracy. Also, there is no way to accurately control the starting time of the fuel supply. Thus, it is difficult to positively improve the output power of the internal combustion engine.